Monocrystalline directional sonic transducer



Jan. 7, 1969 H. cs. AAS 3,421,031

MONOCRYSTALLINE DIRECTIONAL SONIC TRANSDUCER Filed Nov. 23, 1966 Claims This invention relates to the generation of high intensity standing waves, such as for the purpose of high frequency deflection of light beams by refraction techniques, and more particularly to an improved transducer therefor.

The art of high frequency deflection of light beams by refraction techniques includes the use of sonic transducers for the production of standing waves of pressure in an optically transparent fluid, preferably having high mechanical compressibility and a high index of refraction, so as to cause high frequency deflection of light beams through the refraction thereof by the pressure wave in the fluid. One limitation on the maximum amplitude of the pressure in a standing wave is turbulent streaming (a net transport of fluid away from the transducer) initiated at the side walls of the fluid cell. This results from the frictional effect of the fluid which moves along the walls of the cell. To overcome turbulence, transducers have been made of a plurality of crystals arranged in a mosaic array (or matrix) so as to provide a complex mode of osecillation which concentrates the pressure in the center of the transducer with very low pressure components at the edges thereof. The low edge pressure reduces the velocity gradient in fluid along the edges of the cell, thereby reducing turbulence. However, the fabrication of such transducers is very difficult due to the fact that the individual elements of the array must be mounted and tuned so that the relative resonances of the various elements and the Q (the quality factor) of the overall transducer are accurately determined. This is very time-consuming and requires highly skilled workmanship and is therefore quite costly. In addition, such transducers comprised of a plurality of crystals arranged in a matrix have not completely resolved the problem of turbulence.

As used herein sonic means mechanical vibrations in the subsonic, sonic and ultrasonic ranges, and these terms may be used interchangeably herein.

Wherefore, the primary object of the present invention is to provide an improved sonic transducer.

Another object of the present invention is to provide a sonic transducer capable of generating standing waves United States Patent 0 having high pressure amplitudes with a minimum of.

turbulence.

Another object of the present invention is provision of a sonic transducer capable of generating high amplitude standing waves with a minimum of undesired transverse mode effects.

According to the present invention, a single crystal transducer configuration consists of a piezoelectric or ferroelectric transducer on which the edges are contoured to reflect the driven mode to the desired complex mode of sonic pressure wave generation. A transducer in accordance with the present invention is capable of generating a high intensity standing wave for the purpose of high frequency deflection of light beams by refraction techniques. The invention substantially reduces turbulent streaming initiated at the side walls of the cell. The present invention provides a transducer having a gradual transition of generated standing wave amplitude from the edges to the center therein.

An additional advantage of the present invention is that it permits the elimination of undesired transverse 3,421,031 Patented Jan. 7, 1969 modes which cause variation of pressure along the light beam path. Even with a complex matrix or mosaic of individually tuned transducers, these transverse modes have heretofore been very difficult to eliminate.

The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of a transducer formed by contouring the edge of a unitary crystal;

FIG. 2 is a semipictorial view, to an exaggerated scale, of the displacement of one surface of a transducer in accordance with the present invention, as determined by interferrometric means;

FIG. 3 is a semipictorial plan view of a transducer in accordance with the present invention shown in the environment of a fluid cell within which the transducer produces standing waves, together with a plot, to scale, of

maximum standing wave pressure versus transverse dis-- tance across the plan view shown in FIG. 3; and

FIG. 4 is a perspective view of another embodiment of the present invention having edge contouring on the ends of the transducer for the purpose of limiting standing waves along the longest dimension.

Referring now to FIG. I, a typical transducer 10 in accordance with the present invention is shown. The transducer therein may comprise a piezoelectric crystal or ferroelectric module on which the edges have been provided with grooves 12. A typical configuration for the design of the transducer in accordance herewith, which is found empirically, may be five centimeters wide, ten centimeters long, and 1.3 centimeters thick. The grooves may be cut atan angle of 45 along the long edges 14 of the crystal, with approximately one half of the edge area ungrooved. A crystal of this configuration is capable of giving a peak to peak light beam deflection in a tetrachloroethylene cell of more than 5 with a light beam path length of ten centimeters when the cell is excited at a frequency of approximately kilocycles. The cell described above has a Q (or quality factor of resonance) of 25. Other configurations may be chosen to suit the particular design parameters of any utilization of the present invention, as is known in the art.

An oscillator 16 may provide electrical excitation to the transducer 10 by means of'suitable conductors 18 and electrostatic plates 20 (shown broken away. in FIG. 1).

. The displacement of the face surface 22 of the transducer 10 shown in FIG. 1 is illustrated in an exaggerated form in FIG. 2. FIG. 2 is an exaggerated approximation of the interferometer pattern obtained when measuring the mechanical activity of the crystal when excited in the fashion described hereinbefore. Thus, there is a relatively high depicts the position of the surface of the transducer during a period when the center lobe is in maximum extension, and the dotted line 26 depicts the position of the surface when the center lobe is in maximum compression. The first side lobes of significant amplitude are nearly, but not quite, out of phase with the center lobe. It is this characteristic of the transducer in accordance with the present invention which eliminates turbulent streaming problems as described hereinbefore.

Referring now to FIG. 3, the transducer 10 in accordance herewith is mounted within a cell 28, having side walls 29 (shown sectioned) which enclosees a fluid 30 such as tetrachloroethylene. Standing waves of pressure will be generated as depicted by. the lines of variable separation 32 shown in FIG. 3. In the lower portion of FIG. 3 is a plot of pressure amplitude versus distance, which plot is in direct correspondencewith the plan view of the cell 28 and transducer 10 illustrated in the upper portion of FIG. 3. Note that the amplitude of pressure which is created in the standing waves within the fluid 30 of the cell 28 is maximum at the center of the cell and tapers gradually to a minimum at the edges thereof. Thus, turbulence is kept at a minimum as described hereinbefore. Light entering the cell perpendicular to the paper will be deflected upwardly and downwardly in alternate half cycles, as viewed in FIG. 3. An alternative form of transducer which reduces standing waves along the long axis of the crystal is illustrated in FIG. 4. Therein, one or more grooves 34 are provided in the end walls 36 of the crystal. By limiting the reflective effects of pressure generated at the ends of the crystal, there is minimum tendency toward generating standing waves as a result thereof. The effective optical path length of the light beam through the deflecting refraction gradient as a result of high fluid pressure is reduced by about 20-25% due to the reduction in pressure at the front and rear surfaces of the cell as a result of grooves 34.

Although the invention has been shown and described with respect to preferred embodiments thereof it should be understood by those skilled in the art that various changes and omissions in the form and detail thereof may be made without departing from the spirit and scope of the invention, which is to be limited and defined only as set forth in the following claims.

Having thus described preferred embodiments of my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

having a pair of rectangular major surfaces separated by edge surfaces with a V-shaped groove in each of two opposite ones of said edge surfaces, said grooves being parallel with said major surfaces,

and'a pair of electrodes attached to said major surfaces.

2. The invention of claim 1 wherein said crystal is piezoelectric.

3. The invention of claim 1 wherein said crystal is ferroelectric.

4.'The invention described in claim 1 wherein each of said edge surfaces has two V-shaped grooves therein.

5. The invention described in claim 1 wherein said crystal additionally comprises at least one groove cut in each one of another, different pair of opposite edge surfaces.

References Cited UNITED STATES PATENTS 2,447,061 8/1948 Franklin 310-9.5

2,699,508 1/ 1955 Fastenau 3109.5

2,943,279 6/ 1960 Mattiat 3 l08.2

3,074,034 1/1963 Crownover 3 lO8.1

3,143,672 8/1964 Mason 3 109.5

3,377,439 4/1968 Rouy 3 l0--9.5

J. D. MILLER, Primary Examiner.

US. Cl. X.R.

1. A transducer comprising a single orthogonal crystal 30 

1. A TRANSDUCER COMPRISING A SINGLE ORTHOGONAL CRYSTAL HAVING A PAIR OF RECTANGULAR MAJOR SURFACES SEPARATED BY EDGE SURFACES WITH A V-SHAPED GROOVE IN EACH OF TWO OPPOSITE ONES OF SAID EDGE SURFACES, SAID GROOVES BEING PARALLEL WITH SAID MAJOR SURFACES, AND A PAIR ELECTODES ATTACHED TO SAID MAJOR SURFACES. 